To save Princess Toadstool, Mario conquers the eight worlds of the Mushroom Kingdom by going to the castle in each to defeat a minion of King Koopa. To reach each castle, Mario battles through three “sub-worlds” by defeating or avoiding King Koopa’s henchmen. If Mario successfully fights his way through the castle and defeats the minion, a Mushroom Retaineris freed. Inside the eighth castle, Mario has a final fight with King Koopa and frees Princess Toadstool.